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1. Field of the Invention
The present invention relates generally to the field of high frequency antennas and more particularly to the field of a parallel-feed, high-gain, planar, high-frequency antenna constructed using inexpensive manufacturing techniques.
2. Description of the Related Art
The wireless communication industry""s foremost objective is to provide antennas having (1) the lowest possible manufacturing costs with consistently uniform performance, (2) high gain, and (3) high directivity.
Conventional dipole antennas, in which each element of half-wavelength radiators are fed in-phase, produce a substantially omni-directional radiation pattern in a plane normal to the axis of the radiators. However, providing such an omni-directional structure on a substantially planar and inexpensive surface, such as a printed circuit substrate, has proven a challenge. Existing attempts to achieve such planarity and performance rely on vias that penetrate the substrate to interconnect a plurality of conducting planes, thereby adding substantially to the cost of the antenna. Extending planar designs over a wide frequency range has proven even more difficult, since many designs only operate over a narrow frequency range.
In existing designs, as the frequency changes, the phase difference between the two dipoles changes, as result of the feed lines having different lengths. For example, U.S. Pat. No. 6,037,911 discloses a phase array antenna in which the a xe2x80x9cdifferent phase feeding is appliedxe2x80x9d by xe2x80x9cchanging the length of the feeding lines approaching the printed dipoles from outside of the printed patch to the phase center (middle of the antenna).xe2x80x9d
Other designs require the construction of vias thru the substrate. U.S. Pat. No. 5,708,446 discloses an antenna that attempts to provide substantially omni-directional radiation pattern in a plane normal to the axis of the radiators. The patent discloses a corner reflector antenna array capable of being driven by a coaxial feed line. The antenna array comprises a right-angle corner reflector having first and second reflecting surfaces. A dielectric substrate is positioned adjacent the first reflective surface and contains a first and second opposing substrate surfaces and a plurality of dipole elements, each of the dipole elements including a first half dipole disposed on the first substrate surface and a second half dipole disposed on the second substrate surface. A twin line interconnection network, disposed on both the first and second substrate surfaces, provides a signal to the plurality of dipole elements. A printed circuit balun is used to connect the center and outer conductors of a coaxial feed line to the segments of the interconnection network disposed on the first and second substrate surfaces, respectively.
However, in order to connect the coaxial cable to the interconnection network, U.S. Pat. No. 5,708,446 requires a via to be constructed through the substrate. This via""s penetration through the substrate requires additional manufacturing steps and, thus, adds substantially to the cost of the antenna.
Furthermore, other attempts require branched feed structures that further increase the number of manufacturing steps and thereby increase the cost of the antenna. A need exists to use fewer parts to assemble the feed so as to reduce labor costs. Present manufacturing processes rely on human skill in the assembly of the feed components. Hence, human error enters the assembly process and quality control must be used to ferret out and minimize such human error. This adds to the cost of the feed. Such human assembled feeds are also inconsistent in performance.
For example, U.S. Pat. No. 6,037,911 discloses a phase array antenna comprising a dielectric substrate, a plurality of dipole means each comprising a first and a second element, said first elements being printed on said front face and pointing in a first direction and said second elements being printed on said back face, and a metal strip means comprising a first line printed on said front face and coupled to said first element and a second line printed on said back face and coupled to said second element. A reflector means is also spaced to and parallel with said back face of said dielectric substrate and a low loss material is located between said reflector means and said back face, whereby said first and second lines respectively comprise a plurality of first and second line portions and said first and second line portions respectively being connected to each other by T-junctions.
However, in order to provide a balanced, omni-directional performance, U.S. Pat. No. 6,037,911 requires a branched feed structure through the utilization of T-junctions. These T-junctions add complexity to the design and, again, increase the cost of the antenna.
Finally, more complex, high frequency antennas have a high loss line structure and, thus, require an expensive dielectric substrate. Due to the simplicity of production and elements and the low cost of the raw materials, the antenna""s cost is significantly lower than for more complicated, high frequency antennas.
To address the shortcomings of the available art, the present invention provides a planar antenna having a scalable multi-dipole structure for receiving, and transmitting high-frequency signals, including a plurality of opposing layers of conducting strips and antenna elements disposed upon either side of an insulating (dielectric) substrate.
In one embodiment, the invention consists of 4 dipoles in a planar configuration. Two dipoles are in a same horizontal level and symmetric on opposite sides of a feedline. This orientation enables achievement of omni-direction coverage of signals radiated from the antenna. An identical pair of dipoles are stacked on top (or below) the original pair. A balanced feedline passes up to a point which is symmetric to all 4 dipole dipoles and splits to 4 balanced feed lines that feed each of the dipoles in-phase.
In another embodiment, the present invention is an antenna that optimized to function between 5.15 and 5.35 GHz frequency range.
Another embodiment of the present invention incorporates two series capacitors coupled to each respective feed structures to help in matching.